Petroleum hydrocarbons (oils) in and on spent catalyst feeds are known to inhibit metal reclaiming economics. The oils present on the catalysts block the catalyst pores and require more severe conditions to oxidize surface metals via hydrometallurgical oxidation. In addition, oils lead to undesirable organic contamination in leaching processes and recovered products. Methods commonly used to deoil catalyst, such as thermal deoiling or roasting, are unsatisfactory, leading to alumina reactions with metals at high temperatures and ultimately reduced metal yields.
Metals targeted for reclaiming are commonly recovered following removal of in-use generated petroleum coke. Coking of hydrotreating catalyst does not limit the metals recovery, but may impact processing kinetics due to catalyst pore plugging. The coke may impact reaction kinetics in hydrotreating by lowering diffusion rates due to catalyst pore plugging. Removal of the coke is costly and requires high temperature processing of 400.degree. C. to 800.degree. C. At the higher temperatures, the reaction is fairly rapid, making the process impossible to do in a gradual, controlled manner. Further, the process, which is exothermic at the surface of the catalyst, thermally stresses the catalyst surface and converts metals to less soluble species such as spinels. Therefore, a low temperature, controlled process is desirable.
To meet present day standards as a total reclaimer, oil must be recovered as a commercial product. The oil cannot be rendered as a waste stream in the deoiling process. In conventional high temperature treatments the oil is burned off with the coke, emitting carbon dioxide, carbon monoxide, and sulfur and nitrogen oxide byproducts. A more robust reclamation process minimizes air emissions and provides for recovery of the oil as a value-added product.
Metals present on the catalyst are present as a range of sulfides located in a variety of surface geologies. Some of the metal sulfides are readily oxidized in air at ambient temperatures, but other metal sulfides may require elevated temperatures and oxygen pressures to oxidize.